1. Field of the Invention
Embodiments described herein generally relate to methods and apparatus for stabilizing a downhole tool during a downhole operation. Particularly, the embodiments relate to an expandable stabilizer adapted to contact the interior of a tubular in a wellbore during a downhole operation. More particularly, the embodiments relate to a fluid actuated stabilizer that is offset from a radius of a body of the stabilizer in order to improve stabilization while increasing the life of the stabilizer and downhole tool.
2. Description of the Related Art
During the drilling and production of oil and gas wells, a wellbore is formed in the earth and typically lined with a tubular that is cemented into place to prevent cave ins and to facilitate isolation of certain areas of the wellbore for collection of hydrocarbons. During drilling and production, a number of items may become stuck in the wellbore. Those items may be cemented in place in the wellbore and/or lodged in the wellbore. Such stuck items may prevent further operations in the wellbore both below and above the location of the item. Those items may include drill pipe, packers, and downhole tools. In order to remove the item, milling tools are used to cut or drill the item from the wellbore.
Typical milling tools have blades located on the lower end of the milling tool. The blades form a cutting surface. As the milling tool is rotated, the cutting surface will cut through the stuck item. The cutting of the stuck item will wear away the cutting surface and eventually require the replacement of the milling tool. The time required to remove and replace the milling tool amounts to a substantial cost due to lost rig time and the equipment costs. Therefore, extending the life of the milling tool greatly increases the cost effectiveness of the milling operation.
A number of factors contribute to the milling tool wear, including blade material, blade configuration, and vibration of the milling tool. Vibration of the milling tool is caused by the milling tool and the milling tool conveyance being of a smaller diameter than a wellbore tubular in which the milling operation is taking place. The smaller diameter of the milling tool creates a clearance area between the tubular and the tool allowing movement of the tool in the tubular. Further, the milling tools are often built significantly smaller than the tubular in order to ensure that the milling tool will pass any restrictions downhole. In addition, often times the tubular that is deeper in the wellbore has a smaller wall thickness than the tubular near the surface of the wellbore. The smaller wall thickness causes the wellbore inner diameter to be larger at the bottom than near the surface. This creates an even larger clearance area between the milling tool and the tubular. When the milling tool is rotated to mill the stuck item, the milling tool and the conveyance move and vibrate rapidly in the clearance area. This vibration greatly reduces the life of the milling tool and decreases the rate the milling tool cuts the stuck item.
Currently, in order to minimize vibration during milling, stabilizers are used in conjunction with the milling tool. Traditional stabilizers were fixed members coupled to the milling tool. The traditional stabilizers have fixed length protrusions extending radially from the stabilizer. These protrusions have an outer diameter of close to the minimum inner diameter of the tubular they were run into. The traditional stabilizers must be small enough to travel within the tubular and therefore always have some degree of clearance between the stabilizer and the inner diameter of the tubular. Though traditional stabilizers are robust, they do little to hamper vibration.
Further, bow spring stabilizers are used to stabilize a milling tool. The bow spring stabilizer is simply a plurality of thin metal sheets located circumferentially around the stabilizer. Once downhole, the bow springs are actuated to bow radially outward and into contact with the internal diameter of the tubular. The bow spring stabilizers are not effective at reducing the vibration in the milling tool. This is due to the bow spring being flexible and allowing vibration to transfer through the bow spring and to the milling tool during a milling operation. Further, the bow spring lacks robustness and is often subject to mechanical failure when debris or restrictions are encountered.
There is a need for a method and apparatus to reduce the vibration of a milling tool thereby increasing the longevity and the effectiveness of the milling tool. There is also a need for an expandable stabilizer that may engage an inner diameter of a downhole tubular during a milling operation. There is a further need for a stabilizer that is compliant in order to take up inner diameter tolerance and/or variation of the wellbore during a downhole operation.